The present invention generally relates to micromechanical or microelectromechanical (collectively xe2x80x9cMEMxe2x80x9d) systems and, in particular, to the provision and use of covers in connection with components or substrate areas of such systems. Such covers extend over and may substantially encase the protected areas or components to protect against particle contamination.
MEM systems include highly miniaturized devices that employ electrical and/or mechanical components formed on a substrate. There are a number of fabrication technologies, collectively known as micromachining, for producing MEM systems. One type of micromachining process is surface micromachining. Surface micromachining generally involves deposition and photolithographic patterning of alternate layers of structural material (typically polycrystalline silicon, termed polysilicon) and sacrificial layers (typically silicon dioxide, termed oxide) on a silicon wafer substrate material. Using a series of deposition and patterning steps, functional devices are constructed layer by layer. After a device is completed, it is released by removing all or some of the remaining sacrificial material by exposure to a selective etchant such as hydrofluoric acid, which does not substantially attack the polysilicon layers.
A potential problem in connection with MEM systems relates to particle contamination. Particle contamination can potentially impair or disable a system by interfering with the electrical signals and/or mechanical movements of some or all of the electrical and/or mechanical devices. Electrostatic components, such as actuators, are particularly susceptible to particle contamination as particles may be electrically attracted to such components and may cause electrical shorts. Various movable elements may be susceptible to mechanical interference due to particle contamination. Such contamination can occur during construction/assembly or during operation. Completed systems are typically packaged so as to reduce exposure to potential contaminants from the ambient environment, but significant levels of contaminants may still occur within such packaging, thereby reducing yield and potentially allowing for malfunctions after system deployment. In many environments, including MEM-based optical switches, such malfunctions could entail substantial expense and inconvenience, e.g., associated with switch down time, network reconfiguration and repair or replacement.
The present invention is directed to shielding components of a MEM system or substrate areas (together with any overlying structure) from particle contamination. In this manner the yield and reliability in operation of MEM systems can be improved. Additionally, reduced susceptibility of MEM systems to particle contamination allows for construction and assembly of MEM systems under more practical conditions relating to cleanliness, thereby reducing costs. The invention thereby facilitates more practical and cost effective MEM system construction and assembly, including for high criticality applications such as MEM-based optical switches.
In accordance with one aspect of the present invention, a cover is provided to protect an active component of a MEM apparatus from particle contamination. The cover extends over and, preferably, substantially encases the active component. The associated MEM apparatus includes a substrate, an active component formed on the substrate, and a cover formed on the substrate and extending over the active component. An associated process involves establishing an active component on a substrate and establishing a cover on the substrate extending over the active component. The active component and cover are preferably formed on the substrate by a surface micromachining process.
The active component may include an electrostatic element and/or a movable element. In this regard, an electrostatic actuator is an example of a component that includes both electrostatic and movable elements. As noted above, electrostatic elements are a particular concern with respect to particle contamination because such elements may attract charged particles and such particles may cause short circuits or other malfunctions. In this regard, electrostatic components include components that receive a voltage in operation such that an electrical potential is established relative to other components or structure of the device. Similarly, movable elements are a concern with respect to particle contamination because particles may mechanically interfere with movement.
The cover may extend over the entirety of the active component or over an area of the component, e.g., a critical area with respect to movement or likelihood of particle attraction. It will be appreciated that in some cases, such as typical actuator implementations, the cover will include openings or otherwise terminate so as to allow the covered component to mechanically and/or electrically interface with cooperating elements. Moreover, the cover may be an uninterrupted web of material or may be intermittent (e.g., formed as a grid or screen) or otherwise include openings. In this regard, openings may be provided to facilitate penetration of an etchant during a release process. In cases where the cover includes openings, such openings are preferably dimensioned to minimize penetration of potentially harmful particles, e.g., having a maximum dimension of less than about 5 microns and, more preferably, less than about 2 microns. Filters may be provided in connection with such openings to further reduce the potential for particle contamination.
In one embodiment, the MEM apparatus is an optical control apparatus such as for moving a micromirror, microlens, shutter or other movable optical component. The apparatus includes: a movable optical component; an actuator mechanism, formed on a substrate, for effecting movement of the optical component; and a cover supported on the substrate and extending over the actuator mechanism. The actuator is preferably movable in response to electric control signals and may include at least one electrostatic element and at least one movable link for use in transmitting motion to the optical component. The cover may extend over at least a portion of the electrostatic element and/or link. Such an apparatus may be implemented in connection with micromirror-based optical systems such as 1xc3x97N or Nxc3x97N optical cross-connect switches, multiplexers, demultiplexers, spectrometers, etc.
It has been recognized that structural issues have the potential to interfere with successful implementation of covers, or other large area structures, for certain applications. In particular, in order to provide the desired particle protection in connection with certain components such as certain electrostatic actuators, the cover may be required to extend over a substantial area, e.g., the cover may have a maximum dimension of greater than hundreds of microns or even greater than several millimeters. In such cases, the cover may be drawn along an axis transverse to the substrate surface (e.g., down towards underlying structure) so as to potentially cause short circuits or otherwise interfere with operation of adjacent components or prevent proper release. This may be a particular concern where the cover extends over very large areas or where the cover extends over electrostatic elements that may attract the cover. Other forces that may act on the cover include meniscus forces, stiction and loads from interconnected structure.
In this regard, in accordance with another aspect of the present invention, at least one support structure such as a post is used to support an overlying structure of a MEM apparatus. The corresponding apparatus includes: a substrate; an active component supported on the substrate and extending across a first area of the substrate; an overlying structure supported on the substrate and extending over the first area; and a support structure disposed in the first area for supporting the overlying structure. The active component may include an electrostatic and/or a movable element. The overlying structure may be a cover or other element. The support structure preferably extends across space occupied by active component between the overlying structure and the substrate. For example, the support structure may extend from the substrate to the overlying structure.
The support structure can be implemented so as to minimize the potential for electrical or mechanical interference with the active component. In this regard, where the active component includes movable elements, the position of the support structure can be selected with due regard for the expected range of motion of the movable elements so as to avoid mechanical interference between the support structure and movable elements. Where the active component includes electrostatic elements, the support structure may be configured to avoid disruption or contact with elements and/or may be otherwise electrically isolated therefrom.
According to another aspect of the present invention, an electronic filter may be integrally formed as part of a MEM apparatus. Various types of MEM devices include conductors for transmitting signals such as control signals for controlling movement or other operation of active components. In some cases, very accurate control of these components may be required. Unfortunately, high performance microelectromechanical actuation systems may be susceptible to very low levels of electrical noise or other artifacts of the control signals. The potential for such problems increases with progressive miniaturization.
An apparatus according to this aspect of the present invention includes: a substrate; an electrical conductor supported on the substrate; and a filter formed on the substrate for filtering artifacts from an electrical signal transmitted by the conductor. For example, the filter may function to apply a capacitance in the pathway of the conductor or in parallel with an electrical feature of the conductor pathway. The filter may thereby provide a frequency dependent filtering function. In one embodiment, filter material is formed in proximity to the conductor but separated from the conductor by air or insulating material. The filter material may be grounded or otherwise controlled to have desired characteristics. A capacitance is thereby established between the conductor and adjacent structure. The capacitance may be selected to impart desired filtering characteristics, e.g., through appropriate selection of materials, dimensions, configurations and electrical properties.